In general, in accordance with Orwell's rules, prefer the active voice to the passive voice.
Though it was once an area of some debate, I think it's fair to say that most people recommend against using the passive voice in technical writing. But it is still common to see or hear 'these experiments were performed' or 'the following conclusions can be drawn', instead of the active voice: 'we performed these experiments' or 'I draw the following conclusions'.
Writers certainly overused the passive voice in the past. Result: scientific texts are often boring to read, with a detached, impersonal feel. Geoscientists might arguably feel especially tempted to detach themselves in this way, because the strong element of interpretation feels unscientific. But you're only kidding yourself: be bold about your professional assertions and tell your audience what you did.
Personally I find this one of the hardest things to do; I have to remind myself constantly. One way to try to reduce the passive voice in your writing is to go through your manuscript and underline every time any form of the verb 'to be' comes before another verb. Words like 'is', 'are', 'were', etc, are good signals that the passive voice is being used (did you spot that one?).
Then re-write the most obnoxious occurrences, and you will have improved your manuscript substantially.
Try the method on this passage:
It has been shown that seismic data can be processed to much wider angles than previously thought. This development has obvious utility in the oil sands, where the reservoir is very shallow and the reflection angles are necessarily wide. For the time being, it is proposed to use these wide angles only for imaging; we hope also to apply them to other problems later.